Extended abstract TAPPI Nanotechnology 2010, Espoo Printed electrodes on tailored paper enable electrochemical functionalization of paper Jouko Peltonen1, Anni Määttänen1, Roger Bollström1, Martti Toivakka1, Ulriika Mattinen2, Milena Stępień1, Johan Bobacka2, Jarkko Saarinen1, Petri Ihalainen1

1Center of Excellence for Functional Materials (FunMat), Laboratory of Paper Coating and Converting, Åbo Akademi University, Turku, Finland 2 Process Chemistry Centre, Laboratory of Analytical Chemistry, Åbo Akademi University, Turku, Finland Currently most of the applications of printed functionality are established on plastic films. However, the recyclability of such devices is poor. A more sustainable alternative is to use paper as the printing substrate. For example, a thin, lightweight, and foldable thermochromic display has been realized on a regular copy paper [1]. It has also been shown that a transistor can be realized on a paper substrate by an all-printing process [2]. The barrier and printability properties of such a paper substrate are controlled by separate coating layers. The choice of the pigment as well as the thickness (0.5-10 µm) and porosity of the top coating together with the barrier layer underneath the top coating provide controlled sorption and printability properties. Electrodes printed on this kind of a paper substrate can be applied in liquid environment for electrochemical applications. In the first case study, we demonstrate electrochemical polymerization of Poly(3,4-ethylenedioxythiophene) doped with chloride (PEDOT-Cl) on paper with printed silver (Ag)/polyaniline (PANI) as a working electrode. During galvanostatic deposition, the potential of the electrode was measured at a constant current density (0.08 mA/cm2). The potential-time transient curve for printed Ag/PANI electrode showed three different regions. An initiation region, where potential changed sharply with time, corresponded to the charging of the double layer (including oxidation of PANI) and the formation of PEDOT-Cl nuclei [3]. The growth of the polymer layer continued in the second region where the potential remained approximately constant at about 0.98 V. This initial time-potential transient was similar to that observed for electropolymerization of PEDOT-Cl on platinum [4]. In the third phase the potential slowly increased with time up till the end of the experiment. The quality of the deposited PEDOT-Cl film was analyzed by AFM and ToF-SIMS. As a second case study, electrochemical actuation of liquids by an external electric field (electrowetting) is shown. In electrowetting, one is generally dealing with droplets of partially wetting liquids on planar solid substrates. In most applications of interest, the droplets are aqueous salt solutions [5, 6]. In another approach, an electric field may also be used to modify the surface energy of the substrate on which a drop of liquid is brought. Chibowski et al. have shown that surface energy of minerals, e.g. CaCO3 and Al2O3 can be influenced by an external electric field [7, 8]. This situation is analogous to the system of this study, where a droplet of liquid is placed on pigment-coated paper between two electrodes. The voltage-induced increase of wetting (decrease of contact angle) indeed was found to take place in the direction parallel to the electrodes, strongly indicating, that the surface

energy of the substrate was modified. Compared with MilliQ water, similar kind of effect was observed for poly-DADMAC, for which, however, the change of contact angle was dependent on, and become slower with increasing concentration of poly-DADMAC. The presented results show that a paper substrate with controlled smoothness, barrier properties and surface energy is suitable as a printing substrate for functional inks like metals and conducting polymers. The print characteristics may be tuned by the choice of the top coating parameters like type of pigment, layer thickness and pre-treatment. As a result, printed electrodes together with controlled barrier properties of the paper substrate enabled the demonstration of various applications in liquid environment. The paper substrate provides a cheap, flexible and sustainable platform for developing various functional devices for e.g. printed electronics, sensors and smart packages. References 1. A. C. Siegel, S. T. Phillips, B. J. Wiley, G. M. Whitesides, Lab Chip 9 (2009) 2775. 2. R. Bollström, A. Määttänen, D. Tobjörk, P. Ihalainen, N. Kaihovirta, R. Österbacka, J. Peltonen, M. Toivakka, Organic Electronics 10 (2009) 1020. 3. R. Greef, R. Peat, L.M. Peter, D. Pletcher, J. Robinson, Instrumental Methods in Electrochemistry, Ellis Horwood: Chichester, UK (1985). 4. J. Bobacka, A. Lewenstam, A. Ivaska, (2000), J. Electroanal. Chem. 489 (2000) 17. 5. G. Lippmann, (1875), Ann. Chim. Phys. 5 (1875) 494. 6. F. Mugele, J.-C. Baret, J. Phys.; Condens. Matter 17 (2005) R705. 7. E. Chibowski, L. Holysz, W. Wojcik, Colloids and Surfaces A 92 (1994) 79. 8. M. Lubomska, E. Chibowski, Langmuir 17 (2001) 4181.

Printed electrodes enable electrochemical

functionalization of paperfunctionalization of paper

Presented by:

Jouko PeltonenProfessorÅbo Akademi University

OUTLINEOUTLINE

IntroductionIntroduction

Paper substrate for printed functionalityPaper substrate for printed functionality

Printed electrodesPrinted electrodes Printed electrodesPrinted electrodes

ElectrodepositionElectrodeposition of PEDOTof PEDOT--ClCl

Electric field assisted wettingElectric field assisted wetting

SummarySummary

Dimensional stability,

flexibility, smoothness

Purity, chemical resistance, wetting &

IntroductionIntroduction

PrintedPrinted functionalityfunctionality and ”and ”paperpaper electronicselectronics””

Plastics vs. paper? Plastics vs. paper?

Paper & board typically

– rough, porous, absorptive and resistance, wetting & adhesion properties

Barrier properties

Printability

Availability, recyclability, disposability

Price

– rough, porous, absorptive and chemically heterogeneous

+ widely available, flexible, low-cost, sustainable, printable

“It would be more appropriate if 50% of the development money was aimed at electronics on paper”

Peter Harrop, IDTechEx Ltd, 2009

Paper Paper substratesubstrate for for functionalfunctional printingprinting

Calendered clay topcoating

RMS 55 nmBasepaper

90 g/m2

PrecoatingSmoothing layer 7.0 g/m2

Barrier layer 20.0 g/m2

Topcoating 3.0 g/m2 - thickness 0.5-10 µm

- pore diameter 40-100 nm

- surface energy 27-45 mN/m

Subsequent coating layers provide controlled barrier Subsequent coating layers provide controlled barrier properties and smoothnessproperties and smoothness

SA latex barrier layer

RMS 260 nm

90 g/m

GCC Precoating

RMS 580 nm

Clay smoothing layer

RMS 300 nm

Washed Mylar® A

RMS 30 nm

R. Bollström et al., Organic Electronics 10 (2009) 1020.R. Bollström et al., Patent application FI(20095089), (2009).

20 x 20 µm2

Mapping of material properties by harmonic mode AFMMapping of material properties by harmonic mode AFM

Topograph

Kaolin-SB latex coated paper (2.5 x 2.5 µm2)

Elastic modulus map Adhesion map

Paper substratePaper substrate

P. Ihalainen, J. Järnström, A. Määttänen, J. Peltonen, Colloids Surfaces A, submitted

Local mechanical properties influence print quality (e.g. rotogravure ) Local chemical properties important e.g. for inkjet, (cf. Cassie surfaces)

Z-scale: 600 nm Z-scale: 5 Gpa Z-scale: 30 nN

CassieWenzel

Printability of a semiconductor ink by inkjetPrintability of a semiconductor ink by inkjet

Paper substratePaper substrate

Ink: 0.5 wt.% P3HT in o-dichlorobenzene (o-DCB)

P3HT

Määttänen et al., Colloid Surfaces A 367 (2010) 76-84

Määttänen et al., Industrial and Engineering Chemistry Research (2010), submitted

0,45

0,50

0,55

KaolinC

KaolinB

PET

mica

[m

m]

5 µm2 µm

Paper substratePaper substrateSpreading kinetics of a semiconductor inkSpreading kinetics of a semiconductor ink

Ink: 0.5 wt.% P3HT in o-dichlorobenzene (o-DCB)

Määttänen, et al., Colloid Surfaces A 367 (2010) 76-84

Sz

Maximal spreading of inkjet droplets (radius R) of o-DCB is dependent on roughness, surface energy, pore volume and geometry of the paper coating.

The wetting rate (slope) correlates with the magnitude of surface extremes (asperities, Sz)

-1,8 -1,2 -0,6 0,0 0,6 1,2 1,8 2,4 3,0

0,30

0,35

0,40

Barrier

PCCB

PCCA

KaolinA

KaolinB

log

R [

mm

]

log t [s]

2 µm1 µm10 µm 3 µm

Topography, conductivityTopography, conductivity

Electrodes printed on paperElectrodes printed on paper

Ag comb structure:

- Line width 185 µm

- Gap 595 µm

Silver

Precoat

Barrier layer

Smoothing layer

Topcoat

Määttänen, et al., Colloid Surfaces A 367 (2010) 76-84

Silver ink for inkjet:

Silver content 20 wt%

Viscosity 10-13 cps @ 25 °C

Surface tension 27-31 dynes/cm

Resistivity: 20-60 µΩcm(nominal value 5-30 µΩcm)

Base paper

Precoat Smoothing layer

Precoat

Transistor printed on paper Transistor printed on paper

Printed Hygroscopic Insulator FET (HIFET)Printed Hygroscopic Insulator FET (HIFET)

I-V Characteristics

A transistor being stored for 4,5 months in room atmosphere

Moisture absorbed in the PVP layer makes the ions mobile enhancing device operation through enhanced gate field modulation.

Mobile negative ions moving into PVP/P3HT interface may cause electrochemical doping of the semiconductor.

R. Bollström et al., Organic Electronics 10 (2009) 1020.

GalvanostaticGalvanostatic electropolymerizationelectropolymerization

Electrochemical depositionElectrochemical deposition

Electrodes printed on paper offer a practical and cost-effective solution for e.g. sensors based on electrochemical detection.

A three-electrode cell setup

based on electrochemical detection.

The setup is simple with RT operation, and allows reproducible film deposition with highly controllable film thickness.

Printing of Ag/PANI working electrodesPrinting of Ag/PANI working electrodes

AFM: PANI layer

thickness ~1.5 µm

pore depth ~300 nm

Electrochemical depositionElectrochemical deposition

Ag flexographically printed

PANI (A = 1 cm2) inkjetted

Resistance over PANI layer ~ 50 Ω

pore depth ~300 nm

ToF-SIMS: Ag/Pani border

Polyaniline is fully covering the silver electrodes

Ihalainen et al. Thin Solid Films, submitted, 2010

0.1 M KCl + 0.01 M EDOTconstant current I = 35 µAcurrent density 0.08 mAcm-2

Electrochemical depositionElectrochemical deposition

Double-layer charging and formation of PEDOT-Cl nuclei on paper slightly slower than that on tin oxide

Ihalainen et al. Thin Solid Films, submitted, 2010

Characteristics of the deposited PEDOTCharacteristics of the deposited PEDOT--ClCl layerlayer

Dark-blue círcular area marks PEDOT-Cl layer

AFM (20×20 µm2):

3D clusters, height 0.2-3 µm

Heterogeneous

Electrochemical depositionElectrochemical deposition

Ihalainen et al. Thin Solid Films, submitted, 2010

Heterogeneous growth

SEM/EDS:

Presence of sulfur and chloride

An electric field can be also used to modify the surface energy of a substrate .

Electric field assisted wettingElectric field assisted wetting

Modifying the wetting of a liquid on a solid substrateModifying the wetting of a liquid on a solid substrate

Wetting properties of a liquid can be modified by an external electric field.*

change in liquid’s surface tension gives modified Young’s eguation:

An electric field can be also used to modify the surface energy of a substrate .

Chibowski et al.** have shown that surface energy of minerals (e.g., CaCO3, Al2O3) can be influenced by applying an electric field

electron donor and acceptor components change due to the reorientation of the hydrated water molecules

We use pigment-coated paper and the electrodes printed on it for demonstrating electric field assisted wetting.

** Chibowski, et al. Colloids Surfaces A 92, 79 (1994); Lubomska, et al. Langmuir 17, 4181 (2001)

* G. Lippmann, Ann. Chim. Phys. 5, 494 (1875); F. Mugele et al. J. Phys.: Condens Matter 17, R705 (2005)

Experimental setExperimental set--upup

Liquid: MilliQ water (18 MΩcm)

Substrate: GCC- coated paper

Electrodes: Flexoprinted silver

Electric field assisted wettingElectric field assisted wetting

Saarinen et al., NPPRJ, submitted, 2010

Wetting enhanced only towards paper substrate, caused by the change in surface energy.

SummarySummary

While having some short-comings as a substrate, paper and board have a few advantages over plastic substrates:

Better control of surface energy and wetting

Allows for online infrared sintering of metal inks

Environmentally friendly, compostable, widely available Environmentally friendly, compostable, widely available

Improved understanding of what is required from a substrate for printability of functional inks has been gained

A number of phenomena and printed functional device concepts demonstrated on paper open up many interesting applications

Acknowledgements

The Academy of Finland

The Finnish Funding Agency for Technology and

Innovation (Tekes)Innovation (Tekes)

Co-authors: Anni Määttänen, Roger Bollström, Martti Toivakka, Milena

Stepien, Jarkko Saarinen, Petri IhalainenUlriika Mattinen, Johan Bobacka

Thank youPRESENTED BY

Jouko PeltonenJouko PeltonenProfessorÅbo Akademi Universityjouko.peltonen@abo.fi